Presumably you used the same ISO image to make the installation DVD and the installation USB, so if there's something wrong with that file, it could cause this problem. Did you MD5 test the ISO image you downloaded? If so, please edit your question to include the result. If you didn't, please do so now, and then update your question with the result.
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Eliah KaganDec 22 '12 at 6:46

1 Answer
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Welcome to Ask Ubuntu! Whilst this may theoretically answer the question, it would be preferable to include the essential parts of the answer here, and provide the link for reference.
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Eliah KaganDec 22 '12 at 6:39